AACE: Insulin Sensitizers May Protect Colon

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Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

Explain that use of insulin sensitizers like metformin and thiazolidinediones may prevent the development of colon polyps in patients with type 2 diabetes, according to a retrospective study.

SAN DIEGO -- Use of insulin sensitizers like metformin and thiazolidinediones may prevent the development of colon polyps in patients with type 2 diabetes, according to a large retrospective study.

In the study of more than 132,000 VA patients with type 2 diabetes undergoing colonoscopy, there were lower odds of having polyps among those on either metformin (OR 0.95, 95% CI 0.91 to 0.98) or thiazolidinediones (OR 0.83, 95% CI 0.78 to 0.87), reported Deepti Bulchandani, MD, a fellow at the University of Kansas in Kansas City.

"As far as we know, that has not been seen before," she said at the American Association of Clinical Endocrinologists meeting here. "So this might be one more reason to use insulin sensitizers in such patients even though they have good diabetes control on other medications or on insulin."

Both diabetes and the use of exogenous insulin have been associated with a greater risk of colon cancer.

Because most colon cancers arise from polyps, Bulchandani and her colleagues set out to identify predictors of polyp development in patients with type 2 diabetes.

The team looked at data from 132,354 patients with type 2 diabetes who were undergoing screening colonoscopy at one of 10 VA Veterans Integrated Service Networks from 2003 to 2008. The mean age of the patients was 63 and nearly all were male (96.9%). The average HbA1c was 7.15%.

Overall, 41.4% of the patients had a polypectomy.

After adjustment for Charlson comorbidity score and HbA1c, there were several predictors of the presence of polyps, including increasing age, male gender, non-Hispanic white race, and tobacco use.

In addition, having an HbA1c above goal (6.5% and higher) was also associated with polypectomy (OR 1.06, 95% CI 1.03 to 1.09).

That underscores the importance of good diabetes control, Bulchandani said, which "not only prevents all these other complications but may prevent colon polyps and a future risk of colon cancer."

The use of various medications, including aspirin, insulin sensitizers, sulfonylureas, and non-steroidal anti-inflammatory drugs (NSAIDs) was also associated with lower odds of polypectomy.

The strongest relationships were seen with NSAIDs (OR 0.63) and thiazolidinediones (OR 0.83).

Bulchandani said that if the association between insulin sensitizers and lower odds of having colon polyps is proven causal, the mechanism likely involves endogenous hyperinsulinemia caused by insulin resistance, and that the outpouring of insulin is probably a promoting factor for the development of polyps.

Insulin sensitizers prevent endogenous hyperinsulinemia from occurring, possibly eliminating the downstream effects of polyp formation and the development of colon cancer, she added.

"This might be a very good reason to continue people who are already on an insulin sensitizer when other medications are added for diabetes control," she said.

Another interesting finding, according to Bulchandani, is the lack of a relationship between exogenous insulin use and the odds of having a polypectomy -- which contrasts somewhat with previous studies that found a link between insulin use and a greater risk of colon cancer.

"I think the linkage between insulin and colon cancer is not very clear," Bulchandani commented.

She added that she and her colleagues plan to prospectively follow these same patients to evaluate any predictors of the future development of colon cancer.

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